For this you will need:
Start off with a base colour. I've gone for a pale green. Pick a fairly light colour so that your robin will show up nicely over the top.
Using a brown polish, paint a small half circle at the tip of your nails.
Then use a red polish to paint a smaller circle inside.
Use a dotting tool to add two small dots for the eyes.
Use a black polish to carefully add two dots inside the eyes.
Use a gold polish and a small dotting tool to add a beak and feet to your robin.
Use a bright red polish to draw on your santa hat.
Use white polish to finish off your hat.
Let this all dry thoroughly and then finish with a top coat.
Voila! Christmas robins!